Linglin Yang

Given a query graph, top-k subgraph matching finds up to $k$ matches in a data graph with the highest scores according to a user-defined scoring function. It has wide applications across many fields, including knowledge graphs and social networks. Due to the enormous search space, existing methods are not efficient enough on large graphs. In this paper, we propose PTAB, an efficient serial algorithm for top-k subgraph matching. It traverses an efficiently pruned search space by topology-aware subspace score upper bounds computed from a novel hop index, which stores the range of node properties in a constrained multi-hop neighborhood of each node. Additionally, PTAB integrates a cost-aware root selection strategy, which chooses query nodes leading to a search process that utilizes the pruning power of the hop index as much as possible. Furthermore, we use a novel edge-cut strategy to handle general query graphs with cycles. We also extend PTAB to a parallel version, PTABP, which further improves performance via multi-threading and enhanced pruning techniques. Experimental results on real and synthetic datasets demonstrate that our methods outperform existing methods.

Subgraph query is a critical task in graph analysis with a wide range of applications across various domains. Most existing methods rely on heuristic vertex matching orderings, which may significantly degrade enumeration performance for certain queries. While learning-based optimizers have recently gained attention in the context of relational databases, they cannot be directly applied to subgraph queries due to the heterogeneous and schema-flexible nature of graph data, as well as the large number of joins involved in subgraph queries. These complexities often leads to inefficient online performance, making such approaches impractical for real-world graph database systems. To address this challenge, we propose NeuSO, a novel learning-based optimizer for subgraph queries that achieves both high accuracy and efficiency. NeuSO features an efficient query graph encoder and an estimator which are trained using a multi-task framework to estimate both subquery cardinality and execution cost. Based on these estimates, NeuSO employs a top-down plan enumerator to generate high-quality execution plans for subgraph queries. Extensive experiments on multiple datasets demonstrate that NeuSO outperforms existing subgraph query ordering approaches in both performance and efficiency.

Given a query graph, top-k subgraph matching finds up to k matches in a data graph with the highest scores according to a user-defined scoring function. It has wide applications across many fields, including knowledge graphs and social networks. Due to the enormous search space, existing methods are not efficient enough on large graphs. In this paper, we propose PTAB, an efficient algorithm for top-k subgraph matching. It traverses an efficiently pruned search space by topology-aware sub-space score upper bounds computed from a novel hop index, which stores the range of node properties in a constrained multi-hop neighborhood of each node. Additionally, PTAB integrates a cost-aware root selection strategy, which chooses query nodes leading to a search process that utilizes the pruning power of the hop index as much as possible. Furthermore, we use a novel edge-cut strategy to handle general query graphs with cycles. Experimental results on real and synthetic datasets demonstrate that our method outperforms existing methods.

A regular path query (RPQ) returns node pairs connected by a path whose edge label sequence satisfies the given regular expression. Given a workload of RPQs, selecting the shared subqueries as materialized views to precompute offline can speed up the online processing. Since the available memory is limited, we define the materialized view selection (MVS) problem for RPQs as minimizing the total workload query cost within a memory budget. To tackle the problem's NP-hardness, we design an efficient MVS algorithm based on heuristics. To prevent redundancies in the selected views, we devise the AND-OR directed acyclic graph with closure (AODC) as the multi-RPQ query plan representation for the workload, which encodes the relations between subqueries. In addition to detecting view redundancy, the AODC also incrementally updates itself during view selection. To support query planning, we design a scalable cost and cardinality estimation scheme for full-fledged RPQs, including Kleene closures. Our method, when applied to the Wikidata Query Logs, shows a 9.73× speedup in the total query processing time compared to ad-hoc processing, using the views it selects.